Fluidized beds having membrane walls and methods of fluidizing

ABSTRACT

A fluidized bed apparatus where at least a portion of the apparatus comprises a membrane wall.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to fluidized beds, and methods of fluidizing. In another aspect, the present invention relates to fluidized bed reactors and to methods of gasification. In even another aspect, the present invention relates to fluidized bed reactors having membrane walls, and to methods of gasification. In even another aspect, the present invention relates to fluidized bed coal gasification and to methods of coal gasification.

2. Description of the Related Art

Fluidization is commonly defined as an operation by which particulate fine solids are transformed into a fluid-like state through contact with a gas or liquid. Fluidized beds are known for their high heat and mass transfer coefficients, due to the high surface area-to-volume ratio of fine particles. Fluidized beds are used in a wide variety of industrial processes such reaction, drying, mixing, granulation, coating, heating and cooling.

In many industrial applications, a fluidized bed consists of a vertically-oriented column filled with granular material, and a fluid (gas or liquid) is pumped upward through a distributor at the bottom of the bed. When the drag force of flowing fluid exceeds gravity, particles are lifted and fluidization occurs.

In a reaction process, a fluidized bed suspends solid fuels on upward-blowing jets of air. The result is a turbulent mixing of gas and solids. The tumbling action, much like a bubbling fluid, provides more effective chemical reactions and heat transfer.

Fluidized bed technology is utilized in coal gasification. There are a number of patent applications which are directed toward fluidized beds and/or coal gasification.

A coal gasification reactor of the type wherein agglomerated coal ash is withdrawn from a fluid reaction bed of finely divided coal without the removal of the finely divided coal particles is disclosed in Jequier et al, U.S. Pat. No. 2,906,608 and Matthews et al, U.S. Pat. No. 3,935,825. These patents are incorporated herewith by reference.

In a coal to gas conversion process of the type referenced, a vessel is provided for a fluidized bed. A gas distribution grid is usually positioned in the vessel and defines the bottom surface of the fluidized bed. The central portion of the grid may be conical or cylindrical in shape and comprises a passage. At the bottom of the passage, a constriction is provided having a fixed opening defining a venturi of fixed throat size to provide a uniform upward gas velocity into the vessel and thus into the fluidized bed. Directing a stream of high velocity gas through the venturi or passage into the reaction vessel causes ash particles in the vessel to agglomerate and eventually discharge through the passage and venturi throat.

U.S. Pat. No. 4,023,280, issued May 17, 1977, to Schora et al., discloses a fluidized bed of material retained in a vessel receives a high velocity gas stream through a venturi orifice and passage to assist in the agglomeration of ash particles. The particles form a semi-fixed bed within the passage upstream from the venturi orifice. The particular dimensions of the semi-fixed bed are dependent, in part, upon the orifice size of the venturi. An iris valve defining the orifice permits adjustment of the cross-sectional area of the orifice thereby controls the velocity of the gas stream through the venturi.

U.S. Pat. No. 4,435,364, issued Mar. 6, 1984, to Vorres, discloses an apparatus for withdrawing agglomerated solids, e.g. ash, from a fluidized bed of finely divided solid hydrocarbonaceous material, e.g. coal, is described. Agglomeration is effected by a high temperature reaction between the inorganic constituents of the hydrocarbonaceous material in the fluidized bed environment. A venturi is utilized to serve as a passage for withdrawing the agglomerated solids from the fluidized bed. Spiral or other descending ridges are positioned on the interior surface of the constricted cylindrical opening of the venturi to permit variable and increased rates of agglomerate discharge with improved separation and classification of the solid materials.

U.S. Pat. No. 4,453,495, issued, Jun. 12, 1984, to Strohmeyer, Jr., discloses an integrated control for a steam generator circulating fluidized bed firing system. The system includes an integrated control means, and particularly at partial loads, for a steam generator having a circulating fluidized bed combustion system wherein gas recirculation means is used to supplement combustion air flow to maintain gas velocity in the circulation loop sufficient to entrain and sustain particle mass flow rate at a level required to limit furnace gas temperature to a predetermined value as 1550 F. and wherein gas recirculation mass flow apportions heat transfer from the gas and recirculated particles among the respective portions of the steam generator fluid heat absorption circuits, gas and circulating particle mass flow rates being controlled selectively in a coordinated manner to complement each other in the apportionment of heat transfer optimally among the fluid heat absorption circuits while maintaining furnace gas temperature at a predetermined set point.

U.S. Pat. No. 4,453,498, issued Jun. 12, 1984, to Juhasz, discloses a gas- or oil-burning warm water, hot water or steam boilers, mainly for the supply of households, communal institutions, and industrial plants, the surfaces of which surrounding the furnace are formed as membrane walls having annular passageways connected by thin plates, the passageways receiving the heat carrying agent.

U.S. Pat. No. 4,454,838, issued Jun. 19, 1984, to Strohmeyer, Jr., discloses a dense pack heat exchanger for a steam generator having a circulating fluidized bed combustion system whereby a bed of solid particles comprising fuel and inert material is entrained in the furnace gas stream. Means are provided for collecting high temperature bed solid particles downstream of the furnace. The dense pack heat exchanger directs the hot collected particles down over heat transfer surface, such surface being a portion of the steam generator fluid circuits. Flow is induced by gravity means. The dense compaction of the solid particles around the fluid heat exchange circuits results in high heat transfer rates as the fluid cools the compacted solid material. The heat exchange surface is arranged to facilitate flow of the solid particles through the heat exchanger.

U.S. Pat. No. 4,462,341, issued Jul. 31, 1984, Strohmeyer, Jr. discloses a steam generator having a circulating fluidized bed combustion system whereby there is provision to admit air flow incrementally along the gas path to control combustion rate and firing temperature in a manner to maintain differential temperatures along the gas path. The initial portion of the gas path where combustion is initiated can be held in one temperature range as 1550 F which is optimum for sulphur retention and the final portion of the combustion zone can be elevated in temperature as to 1800 F to produce a greater degree of heat transfer through the gas to fluid heat exchange surface downstream of the combustion zone.

U.S. Pat. No. 4,745,884, May 24, 1988, Coulthard, discloses a fluidized bed steam generating system includes an upstanding combustion vessel, a gas/solids separator, a convection pass boiler and a heat exchanger positioned directly below the boiler and all of the above elements except the gas/solids separator are enclosed within a waterwall structure having outside waterwalls and a central waterwall common to the reactor vessel on one hand and the convection pass boiler and heat exchanger on the other hand. The close proximity of the components of the system eliminate numerous problems present in conventional multi-solid fluidized bed steam generators.

U.S. Pat. No. 5,277,151, issued Jan. 11, 1994, to Paulhamus, discloses an integral water-cooled circulating fluidized bed steam generation system having a particle separator which is formed by the membrane walls of the reactor chamber. The particle separator has a serpentine configuration which includes a first turn which is capable of causing the solid particles in the flue gas to move toward the rear membrane wall and a second turn which is capable of causing smaller sized solid particles and the flue gas to be disposed between the front membrane wall and the larger sized solid particles wherein the flue gas passes through the solid particles to a discharge conduit which is disposed within the rear membrane wall and wherein the smaller sized solid particles are retained between the front membrane wall and the larger sized solid particles. The particle separator also includes a means for recycling the solid particles from the particle separator to the reactor chamber.

U.S. Pat. No. 5,391,211, issued Feb. 21, 1995, to Alliston discloses an integral cylindrical cyclone and loopseal. The cyclone separator for a solids-laden process gas from a reactor also provides a pressure seal for the reactor. The cyclone includes a main housing with a longitudinal axis. The housing is made of a membrane wall construction having a plurality of tubes arranged around the axis and encased within membrane wall panels. A portion of the tubes are bent outwardly to form an inlet which communicates with the main housing for receiving the solids-laden process gas from the boiler. Solids are separated from the solids-laden process gas as they swirl together in the main housing of the cyclone separator. A partition wall is disposed at the lower section of the main housing around the longitudinal axis for defining an outer chamber and an inner chamber adjacent to the outer chamber. Gas is provided to the outer and inner chambers for creating fluidized beds of the solids in the outer and inner chambers. Solids are passed from the inner chamber to the outer chamber through an underflow port in the partition wall. Solids exit the main housing from an overflow port which communicates with the reactor.

U.S. Pat. No. 5,393,315, issued Feb. 28, 1995, to Alliston, et al., discloses an immersed heat exchanger in an integral cylindrical cyclone and loopseal. The cyclone separator for a solids-laden process gas from a fluidized bed boiler or reactor also provides a pressure seal and heat exchanger surfaces for the reactor or boiler. The cyclone includes a cylindrical main housing with a longitudinal axis. The housing is made of membrane wall construction. A portion of the tubes are bent outwardly to form an inlet which communicates with the main housing for receiving the solids-laden process gas from the boiler or reactor. Solids are separated from the solids-laden process gas as they swirl together in the main housing of the cyclone separator. A partition wall is disposed at the lower section of the main housing around the longitudinal axis for defining an outer chamber and an inner chamber adjacent the outer chamber. Gas is provided to the outer and inner chambers for creating fluidized beds of the solids in the outer and inner chambers. Solids are passed from the inner chamber to the outer chamber through an underflow port in the partition wall. Solids exit the main housing from an overflow port which communicates with the reactor. Immersed heat exchanger surfaces are provided in the outer chamber for removing heat therefrom.

SUMMARY OF THE INVENTION

According to one non-limiting embodiment of the present invention, there is provided a fluidized bed apparatus. The apparatus includes a vessel having a top and bottom, and defining a fluidized bed region. The vessel further comprises a membrane wall.

According to another non-limiting embodiment of the present invention, there is provided a method of fluidizing. The method includes fluidizing while heat is being provided through a membrane wall of the fluidizing vessel.

According to even another non-limiting embodiment of the present invention, there is provided a method of fluidizing. The method includes introducing particles into a fluidizing bed region of a vessel. The method further includes providing heating through a membrane wall of the fluidizing vessel.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic representation of one non-limiting example of a fluidized bed of the present invention.

FIG. 2 is a cutaway side view of a portion of vessel 10 of FIG. 1, showing wall 110 and grid 18 as comprising tubes 202 arranged to from membrane walls 200.

DETAILED DESCRIPTION OF THE INVENTION

A non-limiting embodiment of a fluidized bed of the present invention is shown in FIG. 1, which shows a schematic drawing of a fluidized bed gasifying apparatus or device 100 that includes means for agglomerating ash or particulate in the fluidized bed. Such a device has been described in Jequier et al U.S. Pat. No. 2,906,608 and Matthews et al U.S. Pat. No. 3,935,825, both herein incorporated by reference.

Briefly, device 100 includes a vessel 10 within which a fluidized bed 12 is retained. Vessel 100 further comprises outer wall 110. Pulverized fresh feed coal enters via line 14 and is contained within the bottom portion of the vessel or reactor 10 as a fluid bed 12 having a bed density of about 15 to 30 pounds per cubic foot. The coal within bed 10 is converted by reaction with steam and air to gaseous fuel components. These gaseous fuel components pass from the vessel 10 through a discharge line 16.

A shaped sloped grid 18 is provided within vessel 10 at the bottom of bed 12. Air and steam enter through a line 20 and pass through ports in grid 18 to assist in maintenance of bed 12 in a fluidized state. The ash contained in the feed coal within bed 12 generally settles near the bottom of fluid bed 12 due to its greater density. Thus, the ash particles flow down the sides of the generally conical grid 18 and pass into or enter a withdrawal chamber or particle exit passage 22 that is formed as part of the grid 18.

Referring additionally to FIG. 2 there is shown cutaway side view of a portion of vessel 10 of FIG. 1, showing wall 110 and grid 18 as comprising tubes 202 arranged to from membrane walls 200. The tubes of the membrane wall form a spiral flow path for the heat transfer fluid.

The membrane walls comprise tubes that are generally arranged in large panels or banks of parallel tubes which are connected together with a metal membrane or web continuously interposed between each pair of adjacent tubes in the bank to form a tube wall. It should be understood, that the dimensions for the membrane wall may be any suitable dimensions as desired and appropriate. It should also be understood that the membrane walls may be made of any suitable material by any suitable method.

As a non-limiting example, the tubes may generally have an outer diameter which can range from about 1 inch up to about 3 inches, with a wall thickness which can be up to about 0.5 inch. The web or membrane connecting adjacent tubes to each other generally has a thickness about equal to the wall thickness of the tubes, with the width of the webbing generally ranging from about 0.25 inch to about 0.75 inch. The webs or membranes can be welded to the outer walls of adjacent tubes to form the tube banks; however, the tube and connecting membranes can be, and preferably are, formed together in a single casting operation.

It should be understood that any part or all of device 100 may comprise one or more membrane walls. As non-limiting examples, part or all of wall 110 may comprise one or more membrane walls, and/or part or all of grid 18 may comprise one or more membrane walls.

Referring additionally to FIG. 3, there is shown a schematic of membrane wall 210 as forming wall 110 and grid 18. In the non-limiting embodiment as shown, membrane wall 210 comprises ports 211 and 212 for circulation of a heat transfer fluid.

Referring additionally to FIG. 4, there is shown a schematic of membrane wall 220 as forming grid 18. In the non-limiting embodiment as shown, membrane wall 220 comprises ports 221 and 222 for circulation of a heat transfer fluid.

Referring additionally to FIG. 5, there is shown a schematic of membrane walls 230, 240, 250 and 260 as forming wall 110 and grid 18. In the non-limiting embodiment as shown, each of membrane walls 230, 240, 250 and 260 comprise ports 231 and 232 for circulation of a heat transfer fluid. It should be understood that membrane walls 230, 240, 250 and 260 may be operated independently to provide different heating/cooling zones as desired.

While not shown, it should be understood that any single circulation loop may be provided with more than just a pair of ports, and may be provided with any suitable number of ports to vary/control the circulation as desired.

While not shown, it should be understood that membrane walls may be utilized for other parts of system 100 other than just for wall 110 and grid 18. As non-limiting examples, one or more membrane walls may be utilized to form part or all of coal inlet stream 14, part or all of inlet stream 20, and/or part or all of inlet stream 28. Use of membrane walls at these streams may assist in preheating any reactants. A membrane wall could also be utilized to cool outlet streams 16 and 30, or even to recover heat from outlet streams 16 and 30.

Various methods of the present invention for fluidizing particles include providing heating/cooling to the particles by circulating heat transfer fluid through one or more membrane walls.

A non-limiting example of a method of fluidizing is as follows. It should be understood that velocities, percentages, diameters, flow rates, temperatures, reactant compositions, output gas, and any other operating parameter, may be varied according to the operation desired. The following operating conditions are merely specific to this non-limiting example, and are not meant to limit the claimed invention in any way, shape or form.

The ash particles are contacted within passage 22 by a high velocity air-steam stream having a velocity in the range of about 50 to about 200 feet per second. This high velocity air-steam stream enters the chamber or passage 22 by passing from line 28 and through the narrow throat or orifice 24 of the passage or venturi tube 22. The ash particles may be admixed with a considerable amount of finely divided coal particles and form a semi-fixed bed in the passage 22. Depending upon the type of coal utilized, particle size, and other factors, this semi-fixed bed may have a density generally in the range of about 40 to about 60 pounds per cubic foot.

The semi-fixed bed within the passage 22 protects the sides of the passage 22 from abrasive effects created by the high velocity stream through the throat or orifice 24 and additionally protects the walls of the vessel from localized high temperatures. Also, the air-steam stream entering the throat 24 via an inlet line 28 reacts with coal particles that enter the region of the passage 22 resulting in temperatures of about 100 F to about 200 F higher than the temperature maintained in the fluid bed 12.

The air-steam stream represented by input through passage 22 may constitute in the range of approximately 20-40% of the total air and steam to the bed 12. The remainder enters by way of line 20 and grid 18. Typically, the fluid bed has a temperature of 1800 F-2000 F and the temperature in the region of the passage is about 2000 F-2200 F.

The localized higher temperatures in the region of passage 22 cause the ash particles within the passage 22 to become sticky. As a consequence, the ash particles as they strike each other gradually agglomerate. When they reach a sufficient size and weight, the velocity of air-steam stream entering through the venturi orifice 24 is insufficient to keep the agglomerated particles in a fluid or suspended state. They pass downwardly through the orifice 24 into withdrawal line 30.

The velocity of the inlet gases through the venturi throat 24 may be high compared to the gas velocity at distribution grid 18. This high velocity stream, as mentioned previously, forms a jet or a spout giving rise to a violent and rapid circulation of solids in the zone of the passage 22. The gases passing through the orifice 24 may also contain a higher percentage of the oxident than those gases passing through the distribution grid 18. Thereby, as previously explained, a higher temperature is generated in the zone of the passage 22 and in the middle, but not entirely through the fluidized bed 12.

The present invention has been described mainly by reference to coal gasification. It should be appreciated, that the present invention is not limited to coal gasification, but rather, finds utility in many applications in which fluidizing of particles is desired. 

1. A fluidized bed apparatus comprising: a vessel having a top and bottom, and defining a fluidized bed region; and, an injection grid comprising fluid inlet ports positioned to provide a fluidizing medium to region; wherein at least a portion of the fluidized bed comprises a membrane wall.
 2. The apparatus of claim 1, wherein the membrane wall comprises at least two independent flow paths.
 3. A method of fluidizing comprising: introducing a fluid into a fluidized bed of particles, and providing heat to the particles through a membrane wall.
 4. A method of fluidizing comprising: introducing particles into a fluidizing bed region of a vessel; and, introducing heat to the fluidizing bed region through a membrane wall. 